Power Meters Capture Fuel-Efficiency Data

Astech Electronics' marine torque/power meters have been developed to capture data essential in assessing the fuel efficiency of a ship that is derived from the measurement of propeller shaft torque. Torque is measured using a shaft-bonded strain-gauge bridge protected within a steel split-ring assembly clamped around the propeller shaft.

Signal conditioning electronics housed in the ring digitise measurements at a resolution of 16 bits (one part in 64,000) for transmission via inductive coupling from the rotating shaft, across a 25mm air-gap to a stationary pickup. The pickup simultaneously transmits power back to the electronic circuitry eliminating the need for shaft-mounted batteries. A co-axial cable then links the pickup to a remotely located decoder unit.

Here, the measurement data is converted into RS 485 serial data format before onward transmission by cable to remote display modules typically located on the bridge and in the engine room. Where RPM and power measurement are required, an infrared sensor is incorporated with the pickup and its output is converted at the decoder using the time-interval measurement technique. RPM and computed power displays are then available in addition to torque. Further outputs at the decoder include USB port, voltages or process currents and a log of the total shaft revolutions.

Another use for this system is during a ship's performance trials. For trials applications, Astech has developed a data-logging software package that can be used on a laptop to record and analyse test results. Astech Electronics said it can provide engineering solutions and support to the ship builders and maritime operators seeking to measure and improve the fuel efficiency of their fleet.

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